Fountain solutions containing isopropyl alcohol are well known for use with presensitized lithographic printing plates. Once the desired image and non-image areas are developed on the plate, the plate is coated with gum etch and/or gumming solution. The function of the gum etch and gumming solution is to desensitize the non-image area so that it does not pick up ink during the printing process. The gum etch solution generally consists of gum arabic, phosphoric acid and preservatives and has a pH around 3.0. The gumming solution generally consists of gum arabic and preservative and has a pH around 5.0. But during the printing process the desensitizing coating starts to wears out, thus requiring the application of a fountain solution to apply fresh coating of desensitizing gum.
Scumming, or pickup of ink in non-image areas, can be overcome by applying a fountain solution during the printing process. A thin coating of desensitizing solution known as fountain solution is applied to the plate during printing by a damping system. The fountain solution keeps the non-image areas of the plate desensitized if applied at proper level.
There are three different types of fountain solution: acid, neutral and alkaline. The alkaline and neutral are mainly used in newspaper printing. The acid fountain solution, the most widely used, consists of:
1. Desensitizing agent such as gum arabic, AMBERGUM.RTM. water soluble polymer, etc. PA0 2. Acid such as phosphoric, citric, lactic, tannic, etc. PA0 3. Buffer and corrosion inhibitors such as nitrate, dichromate and phosphate. PA0 4. Wetting agent such as alcohol, surfactant or glycol ether. PA0 5. Preservative. PA0 1. Lowering surface tension to provide better and more uniform wetting of the printing plate with a thinner film of fountain solution. PA0 2. Providing more stable damping, and thus less color variation. PA0 3. Giving a brighter color effect. PA0 4. Providing less ink emulsification. PA0 5. Allowing a rapid achievement of ink/water balance. PA0 6. Preventing moisture transfer to the printing blanket and thus to the paper stock, i.e. less curling of the paper. PA0 7. Eliminating fiber deposits from damping roller covers. PA0 1. Some color pigments in ink were not compatible with an alcohol system. PA0 2. The lacquer-type image base of the presensitized plate could be damaged by alcohol. PA0 3. The high volatility of alcohol provides a risk for building up vapor to toxic and explosive levels in non-ventilated areas. Government pressure on the printing industry to reduce the use of volatile organic compounds (VOC) is increasing. PA0 (1) an aqueous solution of a modified cellulose with a pH below 6.5 wherein a 30% by weight solution of the modified cellulose has a viscosity below 4000 cps at 25.degree. C.; PA0 (2) a desensitizing agent; PA0 (3) an acid and a buffer; and PA0 (4) a wetting agent or surfactant. PA0 (1) preparing an aqueous solution of hydroxypropylcellulose or hydrophobically modified hydroxyethylcellulose having a molecular weight below 100,000; PA0 (2) combining the cellulose solution with ingredients to prepare an acid fountain solution; and PA0 (3) applying the acid fountain solution to a printing plate to control scumming and to improve printing quality.
In acid fountain solutions the pH is kept around 5.0 and isopropyl alcohol generally is used as the wetting agent. The level of alcohol varies between 10-25% by volume depending on the type of press, damping system and temperature at which it is used.
The alcohol in the fountain solution performs the following functions:
The fountain solutions in which alcohol is added by the press people are generally known as two-step fountain solutions. There are some commercial fountain solutions which contain alcohol substitutes and do not require alcohol addition. These are known as one-step fountain solutions.
Yet in spite of all the advantages related to the use of alcohol in commercial fountain solutions, there were some disadvantages such as:
Thus, prior to the present invention a need had existed to reduce or eliminate the alcohol content of commercial fountain solutions. The present invention is directed to filling that need by providing water soluble polymers which can function to replace or reduce alcohol without adverse effect on the printing process as well as to improve the performance of non-alcoholic fountain solutions.